Using old Radio kit

[Andy Day]

Hi Folks, I've just discovered this forum and have the following questions.

I have an old Sprengbrook Sportsman 4 Channel outfit, 35mhz narrow band. It was one of the best outfits of it's era, I bought it when 35mhz was illegal in this country, but we were cheesed off being shot down by 27mhz cb radio and lads with cheap rc cars. This pirate move to 35mhz put pressure on the authorities who eventually changed the rules.

I haven't flown for about 22 years, but now I'n retired a have a reviving interest, probably in Electric power assisted gliders, for which due to cost constraints I'd like to use the old Sprengbrook. I've fitted new cells to the Tx and Rx and they work fine. Now this old outfit is an analogue system, the data  is encoded as a serial string with a period for sync and a frame for each channel whose width can be varied to give servo position. 1 ms plus or minus if i remember correctly.

When I look in the modeling press there is no mention of the encoding or data transmission methods of modern kit. I understand that higher level outfits use a digitaly encoded word to give servo position right through to the servo, but is this true of all modern rc kit?

I see companies offering receivers and servos which are of a manufacture not matching any "combo" manufacturer. how does one know that they will be compatible with ones transmitter? All the servos supplied make no mention of plug compatibility, is there now a standard which is assumed?

[Alistair Taylor]

Plug polarity is pretty much standard now. Central +ve lead flanked by signal and -ve lead. Plug type still varies - Futaba stuff has a lip on the plug, wire colours vary (R/W/B, Yel/B/R, Or/Br/Y).

Avoid old (pre 1990s) Sanwa stuff that uses chunky black plugs - this uses a different polarity (+ve and -ve leads swapped round).

As for compatibility - it's a bit suck it and see. Generally all basic 35MHz FM stuff is compatible, although some mixing functions on transmitters may function slightly differently with different receivers (only to the extent of different slave/master channels).

When you get more complicated (PCM, dual conversion) you're best off using matching gear. I don't know enough about PCM to say what will or wont work.

I did find this on the WWW regarding sprengbrook:

"You can mix xtal types quite happily - I use a JR 3810 tranny with JR, Futaba, GWS, Multiplex, Century, Microprop & Sprengbrook receivers! <img title="EEK!" src="http://static.rcgroups.com/forums/images/smilies/eek.gif" />

I use a JR xtal in the tranny, and the appropriate make of xtal in the receiver - JR xtal in the JR receiver, Futaba xtal in the Futaba receiver etc.

I have had no problems with this setup, flying all sorts of model. Check what xtals are supposed to be used in your Jeti receiver and use that type, using the GWS transmitter xtal in your tranny."

Sorry to mention a different forum but see:

http://www.rcgroups.com/forums/showthread.php?t=364623

In your position I'd use the sprengbrook stuff, then buy a cheap (£10 - 20)  35MHz receiver (e.g. Art-Tech), test it with the sprengbrook transmitter (range in isolation, range when surrounded by other active R/C gear, range when part of electric powered setup), and take it from there.

If you're flying electric assist gliders you have the advantage that if you start to get interference from the motor, you've got a reasonable chance of being able to shut down the motor and land safely.

Oh - and join a local club. You may be able to pick up some handy hints there.

AlistairT

[Andy Day]

Hi thanks for that Alistair. I appreciate the need to test any new rx for compatibility, but I run on a very limited income so  i'm reluctant to spend cash that may be down the drain!

I'd love to join a club but although thats possible - I was in the Ivinghoe Soaring Association - As I'm not allowed to drive any more for medical reasons attending any meets would be difficult, if not impossible. Fortunately I'm mates with a local Farmer and can have an "arrangement", so all I need to sort is insurance. And a big bag to put on my back containing the model when I cycle to his farm!

Of course all my kit is pre - pcm, digitally encoded, failsafes, rates, throw adjustment or anything. Just a plain old FM modulated bitstream with a period for sync, then 4 pulses with varying pulse width for each channel. These pulses are positive going ttl levels, so you may say they are "digital" but apart from being of digital levels, ie a one or zero thats it. Does anyone still sell such technology?

Now a few more specific questions.

Does anyone know if modern servos need a 5volt supply - I suspect they do, or what polarity pulse they need?

With regard to modern FM receivers, all receivers must include a decoder I imagine, does anyone know what sync pulse length they need if there is indeed a standard?

I know these Q's are a bit techie, but after all, the mag is Radio Controlled Models and ELECTRONICS!

[Former Member]

[This posting has been removed]

[Jacques]

If anyone else is reading: 

1) Check your old tx for black wire rot: if it has had a battery in it for all these years, you might find the -ve wire has a black coating of rot which will render it dodgy: replace back to the PCB, as well as possibly replacing the on-off switch and the wiring between the switch and PCB.

2) Replace any nicads : these will be suspect, (cells deteriorate, and the black rot happens in the battery pack too).

3) Before you do that, give Andy Rutter at Micron a ring (01653 696008). He can comment on the coding, but I'm pretty sure that your Tx will be fine given the above. If you are flying "solo" then co-channel interference is not such a problem for you. If it works after range checks: go out and have fun!!

[Derek Ludlaqm]

Help -- I have just recently acquired an old "Spengbrook Variomodul Pilot" transmitter and Receiver and would like to get it up and running again. Unfortunately the power pack is missing and i have no idea what voltage it is, Can anyone help me please.... Also will todays modern crystals fit ? it says that it's 35megs and channel 65. any info would be greatfully received.....Ta Much...